The invention relates to a method of applying a silicon-oxide layer to a substrate, in which method a film of a solution of a polyorganosiloxane in a solvent is applied to a surface of said substrate, whereafter the film is dried, thereby forming a polyorganosiloxane layer which is subsequently converted to said silicon-oxide layer. Such a layer is used, inter alia, as an anti-corrosive or passivating layer on metal surfaces, in particular, of parts of semiconductor devices.
Such a method is known from U.S. Pat. No. 5,057,336. In said known method, a 5 to 30 wt. % solution of a polyorganosiloxane in an organic solvent is provided on a substrate surface, for example, by means of spin coating. The film obtained is dried at an increased temperature, subsequently, heated to a temperature between 100.degree. and 200 .degree. C. and finally to a temperature between 350.degree. and 450 .degree. C. for 60 to 90 minutes. The polyorganosiloxane layer thus obtained has a thickness of 0.4 to 1.5 .mu.m. Subsequently, the layer thus obtained is subjected to an RF oxygen plasma in pure oxygen at a reduced pressure of approximately 1 mbar (1 Torr) for 20 to 30 minutes. Meanwhile, the substrate is heated to a temperature between 200.degree. and 300 .degree. C. This treatment causes the polyorganosiloxane layer to be converted to a pure SiO.sub.2 layer. The layer thickness of the silicon-oxide layer obtained in accordance with the known method is 0.7 .mu.m.
Said known method has a number of disadvantages. It has to be carried out at a high temperature, which is undesirable for certain applications. Particularly metal substrates can oxidize at these high temperatures. In addition, the known method requires expensive vacuum equipment to carry out the plasma treatment. A further disadvantage of the known method is that the silicon-oxide layer obtained is too thick for many applications, in particular applications in which the silicon-oxide layer should hardly, or not at all, adversely affect the electrical resistance.